Display apparatus

Abstract

The present invention relates to an optical system of a small-sized portable display apparatus in which the exit pupil position is relatively spaced apart from the optical system and the exit pupil's diameter is large. A display apparatus comprises a display element 3 for displaying an image, and an ocular optical system 32 for enlarging an image displayed on said display element or an intermediated image thereof as a virtual image, and is characterized in that the ocular optical system 32 has rotationally asymmetric Fresnel surfaces 21, 22.

What we claim is:  
     
         1 . A display apparatus comprising: a display element for displaying an image, and an ocular optical system for enlarging an image displayed on said display element or an intermediated image thereof as a virtual image, said display apparatus being characterized in that said ocular optical system has a rotationally asymmetric Fresnel surface.  
     
     
         2 . A display apparatus as claimed in  claim 1 , being characterized in that said rotationally asymmetric Fresnel surface is composed of a free-form surface.  
     
     
         3 . A display apparatus as claimed in  claim 1 , being characterized in that said rotationally asymmetric Fresnel surface is disposed in a decentered position and is arranged to correct decentration aberrations created due to its decentration.  
     
     
         4 . A display apparatus as claimed in  claim 1 , being characterized in that said Fresnel surface is a Fresnel reflecting surface.  
     
     
         5 . A display apparatus as claimed in  claim 1 , being characterized in that said Fresnel surface is a Fresnel transparent surface.  
     
     
         6 . A display apparatus as claimed in  claim 1 , being characterized by satisfying the following conditional expression: 
       80 mm< EXPe <1000 mm  (1) 
       wherein EXPe is an axial distance from the exit pupil position in said ocular optical system to a surface of said ocular optical system facing the exit pupil.  
     
     
         7 . A display apparatus as claimed in  claim 1 , being characterized in that when the direction of an optical axis is defined by the direction of a Z-axis, the decentering direction of an optical plane is defined by the direction of a Y-axis, and the direction perpendicular to both of the Z- and Y-axes is defined by the direction of X-axis, at least one of said rotationally asymmetric Fresnel surfaces is arranged such that power in the direction of the X-axis and power in the direction of the Y-axis are both gradually stronger with getting closer to the direction toward the position of said display element.  
     
     
         8 . A display apparatus as claimed in  claim 1 , being characterized by further comprising a relay optical system for forming an intermediate image corresponding to the image on said display element, wherein the intermediate image projected by said relay optical system is formed near said ocular optical system.  
     
     
         9 . A display apparatus as claimed in  claim 8 , being characterized in that said relay optical system is made of a medium of which refractive index (n) is greater than 1, i.e. n>1, and comprises an incident facet which allows light beam from said display element to enter a prism, at least one reflecting facet which reflects the light beam inside the prism, and an exit facet which allows the light beam to exit from the prism, wherein said at least one reflecting facet is composed of one or a plurality of decentered prisms having curved surface configurations for imparting power to the light beam.  
     
     
         10 . A display apparatus as claimed in  claim 1 , being characterized in that said ocular optical system has diffusion property.  
     
     
         11 . A display apparatus as claimed in  claim 1 , being characterized in that said ocular optical system has diffusion property at least in one dimensional direction.  
     
     
         12 . A display apparatus as claimed in  claim 1 , being characterized in that said ocular optical system has two axes in different directions, wherein said ocular optical system has diffusion property about each of the two axes.  
     
     
         13 . A display apparatus as claimed in  claim 1 , being characterized in that said ocular optical system has diffraction optical element.  
     
     
         14 . A display apparatus as claimed in  claim 1 , being characterized in that said ocular optical system has hologram optical element.  
     
     
         15 . A display apparatus as claimed in  claim 8 , being characterized by comprising two said display elements, two said relay optical systems to correspond to said display elements, and said ocular optical system which is common to said two relay optical systems.  
     
     
         16 . A display apparatus as claimed in  claim 8 , being characterized in that the position of said display element relative to said relay optical system is adjustable.  
     
     
         17 . A display apparatus as claimed in  claim 8 , being characterized in that said ocular optical system is enable to escape from optical paths so that said display apparatus can be used as a projector.  
     
     
         18 . A display apparatus as claimed in  claim 8 , being characterized in that said position of said display element relative to said relay optical system is adjustable.